1. Field of the Invention
The present invention relates to a vehicular control unit with a self shut-off function and abnormality (or malfunction) detection function in which, even if a self shut-off of a power supply cannot be carried out due to an occurrence of abnormality in the self shut-off function, a power supply turn off (interruption) of the control unit can be carried out without failure.
2. Description of the Related Art
A previously proposed self shut-off function with which each of an engine control unit (ECU), an automatic transmission control unit (ATCU), or any other vehicular control units is provided will be described below. A CPU (Central Processing Unit) of such a control unit as described above receives a power supply voltage (bias voltage) Vcc via a power supply control circuit from an auxiliary ignition power supply which is an auxiliary power supply when an ignition key switch is turned on. When the ignition key switch is turned to OFF and a voltage terminal (E2) of a power supply circuit via which the voltage from the ignition power supply is supplied to the power supply control circuit is turned to be a low level (Low), the same low level voltage is inputted into an A/D conversion input of the CPU. At this time, the CPU starts a self shut-off operation when the A/D conversion input is at the low level. At this time, a battery power supply as a continuous power supply is supplied to the power supply control circuit in place of the auxiliary ignition power supply.
First, CPU executes a shut-off process in which a system operation information is written onto a rewritable nonvolatile memory such as EEPROM (Electrically Erasable Programmable Read Only Memory). Next, the CPU turns a voltage of terminal E1 of the power supply control circuit which is normally at a high level (Hi) to the low level (Low) so that a power down enable signal is outputted to the power supply control circuit. The power supply control circuit, upon receipt of the power down enable signal, stops the power supply voltage (Vcc) to the CPU. Thus, the CPU stops its run due to the interruption of the power supply voltage (Vcc) and, simultaneously, the self shut-off is terminated.